1. Field of the Invention
The present invention relates to a lumbar support mechanism for a vehicle provided with a seat on which an occupant sits and a seat back for supporting the back of the occupant.
2. Description of Background Art
Some motorcycles are provided with a backrest mechanism adjustable for the position of a backrest. See, for example, Japanese Patent Laid-Open No. 2001-315678. This backrest mechanism provides a movable backrest with an elongate member extending toward a raised portion. The raised portion is provided with a void, in which a receiving portion for the elongate member is provided. In the state where a driver has dismounted from the vehicle, while an elongate member is being slid, the position of the movable backrest is adjusted and positioned at an optimal position by means of a bolt or the like. Although backrest mechanisms are available for motorcycles, a lumbar support mechanism capable of adjusting a lumbar spine support position has not been devised. If this backrest mechanism is intended to be applied to a lumbar support mechanism, it is difficult to minutely adjust a lumbar spine support position by the method of manually adjusting the position of the backrest in the state where the rider has dismounted from the vehicle. Thus, it is desired to improve the operability of the backrest. In addition, since the elongate member and the like which are large-sized components are disposed externally of the seat, such a mechanism requires an increase in size.
On the other hand, a lumbar spine support device (substantially corresponding to a lumbar support mechanism) is known that is provided on the backrest lower portion of an automobile seat. See, for example, Japanese Utility Model Publication No. Hei 5-3076. This device includes a base fixedly welded to a seat back frame; a lumbar spine support member supported by the base via a link mechanism so as to be movable forward and rearward; a pair of compression coil springs provided between the base and the lumbar spine member so as to anteriorly bias the lumbar spine support member; and a friction lock mechanism having one end attached to the base and the other end attached to the lumbar spine support member or the link mechanism.
The friction lock mechanism is configured to include a cylinder; a rod inserted into the cylinder so as to be axially movable; a braking member adapted to prevent the movement of the rod while it is wound around the rod and to permit the movement of the rod while it is operated to release the winding; and an operating member for lock-release capable of operation in the direction of releasing the winding of the braking member around the braking member.
The configuration described in Japanese Utility Model Publication No. Hei 5-3076 increases the number of component parts since the spring adapted to push out the lumbar support member (hereinafter, called the pad) and the lock mechanism for specifying the position of the pad are separate from each other. Thus, it is not suitable for small-sized and lightweight vehicles, particularly, such as motorcycles.
Although the lock mechanism locks the link mechanism, it does not lock the springs. Therefore, even in the locking state, the pad may not be supported stably because of an inclination or the like depending on the application of force. More specifically, since the pad is swingably connected to the link member and is biased by the pair of springs, if force is applied to a portion of the pad, the pad is easily swung. Further, since the base is welded to the seatback frame, attachment-detachment work of the mechanism is cumbersome.